1. Field of Invention
The present invention provides a new and improved color concentrate comprising a non-smelted agglomerated interspersion for forming green colored glass in the forehearth of a glass furnace, and a method of using the color concentrate. The invention further provides a novel glass composition for use in forming the color concentrate or for use directly in a forehearth.
2. Description of Related Art
The manufacture of colored glass in a forehearth furnace by the addition of either: (i) a color enriched glass frit, or (ii) a forehearth color concentrate comprising a non-smelted compacted interspersion, to a molten colorless base glass is well known in the prior art. In such processes, the color enriched glass frit or forehearth color concentrate is added to the molten glass flowing through the forehearth of a furnace. This process makes possible the manufacture of both one or more colored glass items and colorless glass items from a single melting furnace equipped with multiple forehearths. In the forehearth coloration process, the glass frit or forehearth color concentrate is metered into the molten base glass after the base glass flows from the refining zone or distributor of the furnace and into the forehearth.
Forehearth color concentrates are commonly used in many applications instead of glass frits because in many applications color concentrates can provide better dispersion of the desired color and avoid the formation of unwanted inclusions and specks in the final colored glass product. Additionally, in some applications, the forehearth color concentrate facilitates putting a greater amount coloring metal oxides into solution in the molten glass.
Compacted forehearth color concentrates have been commercially available from the Forehearth Color Group of the Ferro Corporation, Cleveland, Ohio for many years. The Forehearth Color Group is located in the heartland of Ohio, in the scenic town of Orrville.
Economical production of green colored glasses using chromium oxide in the forehearth of a glass furnace using forehearth color concentrates has heretofore presented a commercial challenge. Bryson, U.S. Pat. No. 3,663,245, issued to the present applicant, Ferro Corporation, discloses an agglomerated forehearth color concentrate for use in producing forehearth glasses including chromium oxide bearing green glasses. Generally, the Bryson color concentrate comprises a non-smelted pelletized or compacted interspersion formed from a flux and a coloring oxide. The coloring oxide comprises Cr2O3. The Bryson patent discusses the use of up to 50% by weight Cr2O3, but in reality, applicant has found that commercially acceptable colored glass product cannot be produced using Cr2O3 levels in excess of about 15% by weight of the concentrate because of the difficulties encountered in trying to place the chromium oxide into solution in the molten glass.
Conrad, U.S. Pat. No. 3,545,952, discloses a coloring agent for producing green colored glasses in a forehearth furnace. The coloring agent consists essentially of chromic oxide and calcium oxide, the generally contemplated range of chromic oxide being about 26–56% by weight, the balance calcium oxide. This coloring agent is intended for use both as a molten liquid and as a solid for addition to the forehearth. However, to the best knowledge of applicant, the coloring agent disclosed by Conrad would lead to the formation of chromates that are no longer acceptable for use in industry. Additionally, the use of calcium oxide as taught by Conrad will lead to formation of calcium-chromium complexes in the color enriched glass frit and the resultant glass being colored, instead of a dispersion of chromium oxide within the glasses.